Radiocarbon measurement tests on OC/EC fractions of atmospheric aerosol at LABEC

Carbonaceous particles are among the main components of the atmospheric aerosol. They are mainly composed of soot and organic compounds. Large uncertainties still affect the estimates on source contributions, especially for what concerns natural emissions and secondary formation. The identification of natural, biomass burning, and fossil fuel combustion contributions is important for the development of efficient pollution abatement strategies and for the correct assessment of global radiative aerosol effects. 14C analysis on total carbon (TC) in atmospheric aerosol by accelerator mass spectrometry (AMS) is a good tool for the evaluation of the contributions from either fossil fuel combustion or modern sources (i.e. wood burning, biogenic activity). At our latitudes, wood burning has to be considered of anthropogenic origin; thus, further analyses are needed to identify natural and anthropogenic contributions. TC in the aerosol is composed by two main fractions: elemental (EC) and organic (OC) carbon, which have different thermal and optical properties. EC is produced only during combustion processes, while OC can be related to combustion processes or biogenic activity. Szidat et al. (2006) proposed the use of radiocarbon measurements on the separate OC and EC fractions of carbonaceous aerosol as a tool to separate natural and anthropogenic contributions. In the last years, a new sample preparation line for 14C analysis on aerosol was designed and set up at LABEC-INFN. The line was tested for TC: reproducibility, accuracy and background tests were performed, indicating that reliable results can be obtained for total carbon (Calzolai et al.,2010). In this work, the sample preparation line was tested for 14C analysis on OC and EC. Suitable sample pre-treatment procedures and thermal protocols were set up for a correct separation of the two fractions. Two different thermal protocols for EC isolation were tested. A few samples collected in Milan (Po Valley) during wintertime were analysed for TC and its fractions, thus allowing to obtain first indication on the apportionment of carbonaceous sources in the area. References Calzolai G., Bernardoni V., Chiari M., Fedi M., Lucarelli F., Nava S., Riccobono F., Taccetti F., Valli G., Vecchi R., Nucl. Instr. Meth. B, in press Szidat, S., Jenk, T.M., Synal, H.-A., Kalberer, M., Wacker, L., Hajdas, I., Kasper-Giebl, A. & Baltensperger, U. (2006). J. Geophys. Res., 111 D07206 121